Houdini 18.5 Nodes TOP nodes

Local Scheduler TOP node

Schedules work items on the local machine.

Since 17.5

This node is the default scheduler that executes work items on your local machine. This node also runs its scheduled work items in parallel.

This node lets you:

These parameters are not related to the multi-threading of individual processes. To control the multi-threading of Houdini work items, use the Houdini Max Threads parameter.


To execute work items on a farm or on remote machines, use a different scheduler like the HQueue Scheduler.



Global parameters for all work items using this scheduler.

Working Directory

Specifies the relative directory where the work generates intermediate files and output. The intermediate files are placed in a subdirectory. For the Local Scheduler or HQueue, typically $HIP is used. For other schedulers, this should be a relative directory to Local Shared Root Path and Remote Shared Root Path; this path is then appended to these root paths.

Path Mapping


If the PDG Path Map exists, then it is applied to file paths.


Delocalizes paths using the PDG_DIR token.

Path Map Zone

When on, specifies a custom mapping zone to apply to all jobs executed by this scheduler. Otherwise, the local platform is LINUX, MAC or WIN.

Validate Outputs When Recooking

When enabled, PDG will check the output files of work items when the graph recooks, to see if the files still exist on disk. Work items that are missing output files will be dirtied and cook again.

Check Expected Outputs on Disk

When enabled, PDG will look on disk for any expected work items outputs that were not explicitly reported when the work item cooked. Expected outputs for a work item are checkd immediately after the scheduler marks the work item as cooked. Output files that were reported by the work item normally while cooking will not be checked.

Temp Directory


Determines where the local temporary files are written to. Files that are written to this location are needed for the PDG cook, but are not typically the end product and can be removed when the cook completes.

For example, log files and python scripts are some of the files that are usually written during the cook.

Working Directory

Use pdgtemp subdirectory specified in the Working Directory field.

Houdini Temp

Use pdgtemp subdirectory of $HOUDINI_TEMP_DIR.


Use the custom directory specified by in the Custom field.

Append PID

When on, a subdirectory is added to the location specified by the Location parameter and is named after the value of your Houdini session’s PID (Process Identifier). The PID is typically a 3-5 digit number.

This is necessary when multiple sessions of Houdini are cooking TOP graphs at the same time.


The full path to the custom temporary directory.

This parameter is only available when Directory Location is set to Custom.


Total Slots

Specifies the number of available slots for this scheduler to use when executing work items. This also provides some default slot counts based on the detected CPU. A higher slot count means more work items can run at once.

For more information, see limiting resource usage.

Equal to 1/4 of Total CPU Count

Use the number of logical cores divided by four.

Equal to CPU Count Less One

Use the number of logical cores less 1.

Custom Slot Count

Use the number specified in the Custom Slot Count field.

Custom Slot Count

The number of slots available to execute work items. A positive number sets the slot count. A negative number sets the slot count as the total logical CPU cores minus the number specified in this field.

Verbose Logging

Print extra debugging information in job output logs.

Block on Failed Work Items

When this option is enabled the scheduler will block the cook from completing if there are any failed work items in that scheduler. This makes it possible to manually retry those work items, by preventing the PDG graph cook from ending before failed items can be retried. A cook that is blocked on failed work items can still be canceled using the ESC key, the cancel button in the TOP task bar, or the cancel API method.

Job Parms

Job-specific parameters.


You can override these parameters per node with the Edit Parameter Interface. For more information, see Scheduler Job Parms / Properties.



When on, only one single work item is executed at a time.

Slots Per Work Item

When on, sets the number of slots consumed by each work item. Work items are only run by the scheduler if at least this number of slots are available.


The total number of slots that are available to the scheduler is determined by the Total Slots parameter setting.

If some of your tasks consume a lot of computational or memory resources, you can use the Slots Per Work Item parameter to change the maximum number of processes that are run in parallel. For example, if there are 8 slots available as determined by Total Slots, then a maximum of 8 processes will be executed in parallel. However, if Slots Per Work Item is set to 2 on the processor node, then a maximum of 4 processes will be executed in parallel with each task consuming 2 slots worth of resources in the scheduler.

Minimum Available Memory


No Minimum

There is no check for available memory.

MB Available

The minimum available memory in Megabytes. Available memory is the amount of memory that can be used by a process without going into swap.

Percent Available

The minimum available memory as a percentage of the system’s total memory.

Minimume MB

The minimum available memory in Megabytes. Available memory is the amount of memory that can be used by a process without going into swap.

Minimum Percent

The minimum available memory as a percentage of the system’s total memory.


When a work item process terminates with a non-zero exit code, it is marked as failed by default. These parameters change that behavior.

On Task Failure

Determines what happens when a work item fails.

Report Error

The work item fails and an error message is added to the node.

Report Warning

The work item succeeds and a warning message is added to the node.

Retry Task

The work item restarts immediately, according to the Maximum Retries and Retry Count Attribute parameter settings.


The work item succeeds and no message is issued.

Handle All Non Zero

When off, lets you specify a particular exit code with the Exit Code field. All other non-zero exit codes are regarded as failures.

Exit Code

Specifies the exit code that is handled by the On Task Failure parameter setting. All other non-zero exit codes are treated as failures.

This parameter is only available when Handle All Non Zero is off.

Maximum Retries

Sets the maximum number of times the work item will be restarted.

Retry Count Attribute

When on, adds an int attribute set to the number of times the task was restarted.

Task Environment

Houdini Max Threads

When on, sets the maximum number of threads each work item can use. This also sets the HOUDINI_MAXTHREADS environment value which is used by Houdini-based programs like Mantra, Karma, Hython, and HBatch.

Requires GUI Window

Normally, processes are started such that they do not pop up command windows on the desktop when they run. However, some Windows applications require a GUI window.


When on, your work items can run GUI Applications in pop-up windows.

Unset Variables

Space-separated list of environment variables that should be unset in the job environment.

Environment Variables

Additional work item environment variables can be specified here. These will be added to the job’s environment. If the value of the variable is empty, it will be removed from the job’s environment.


Name of the work item environment variable.


Value of the work item environment variable.

See also

TOP nodes